Tubulin, the building-block protein of microtubules, is the target for the action of several antitumor drugs such as, colchicine, vinblastine, maytansine, and taxol. Tubulin is a hetero-dimeric protein consisting of two similar but distinct polypeptides designated alpha and beta. Both alph and beta- tubulins occur in different tissues and species as multiple isotypic forms. The long-term objective of this research project is to increase our understanding about the molecular mechanism by which the antitumor drugs interact with tubulin and microtubules. In Specific Aim 1, different antitumor drugs will be tested for their effects on the in vitro microtubule assembly and dynamics from purified beta-tubulin isotypes. In Specific Aim 2, the interaction of taxol with microtubules will be studied. In specific Aim 3, the interaction of colchicine and some of its high- affinity B-ring-modified analogues with different beta-tubulin isotypes will be studied by using fluorometric method. In Specific Aim 4, monoclonal antibodies will be made against short synthetic peptides with sequences from different regions of beta-tubulin, and these monoclonal antibodies will be used as probes to study the involvement of different regions in the interaction of antitumor drugs with tubulin. In Specific Aim 5, a monoclonal antibody will be made against beta (VI)-tubulin, which is specific for hematopoietic tissues. By using different beta-tubulin specific antibody columns (anti=betaII, anti-betaIII, anti-betaIV, and anti-betaVI) prepared in our laboratory, alphabetaVI tubulin dimers will be purified from hematopoietic tissues, such as, spleen, platelets, and also from cultured leukemic cell lines where betaVI-tubulin is abundant. Since betaVI-tubulin is hematopoiesis specific, studies involving alphabetaVI tubulin may be of great significance for selecting a suitable drug for leukemia. The results of our studies described under Specific Aims 1,2 and 3 and 5 will be of great clinical significance in terms of cancer- chemotherapy. Since the composition of tubulin isotypes change from one tissue to the other, the results might help in tissue-specific selection of drugs. The results of the studies described in Specific Aims 4 will increase our understanding on the mechanism of interaction of the antitumor drugs and will be very important for selecting tissue-specific new anticancer drugs.